1. Field of the Invention
This invention relates to a method for tagging an oleaginous and petroliferous substance so that it subsequently may be identified as to source. More particularly, the invention relates to such a method wherein control of the so-tagged substance is temporarily lost, as when it is stolen, spilled, misplaced or injected down a well and/or into a subterranean reservoir.
2. Description of the Prior Art
Sometimes one has in his control a first oleaginous and petroliferous substance. This control can then be lost. The loss can be deliberate, as when an oil is injected down as well as a power fluid in a method for pumping reservoir oil out of a subterranean reservoir, or when an oil is injected into a subterranean reservoir in an enhanced oil recovery process or in a study of the flow conditions within a reservoir. The loss can also be inadvertent, as when an oil is spilled or stolen. Subsequently, there can come within one's control a second oleaginous substance which is suspected either to be or to contain a portion of the first oleaginous substance. This second oleaginous substance may be oil produced from a subterranean reservoir, discovered under circumstances arousing suspicion that it may be oil previously stolen or spilled, or encountered in any of a number of other circumstances.
Such oleaginous substances are difficult to identify. Some oleaginous and petroliferous substances, such as crude oil, have such a complex structure that their compositions are difficult to define and distinguish from each other. Other such substances, such as fractions of crude oil, have compositions so much alike that one sample from one source is difficult to distinguish from another sample from a different source. In either of the above instances tracing a given sample of oil whose origin is unknown back to its source can prove onerous.
One instance in which control of an oil is deliberately lost is during its use as a power fluid in an oil production method. There are diverse methods for producing oil from an oil-bearing reservoir. If the reservoir does not have sufficient pressure so that a well penetrating the reservoir flows oil in sufficient volume to make production practical, a pump may be installed in the well to lift the oil to the surface. One type of pump which can be used is a downhole production pump activated by hydraulic fluid pressure applied from the surface of the earth. In other instances it may be necessary to inject an enhanced oil recovery medium into the reservoir via an injection well to displace the reservoir oil and drive it to one or more production wells. The enhanced recovery fluid can be a miscible, microemulsion, or micellar solution, a composition which contains oil as well as water, a surfactant and perhaps also a cosurfactant. In still other instances, as in studying the flow characteristics of a fluid passed through a reservoir, it is sometimes desired to inject an oil into a reservoir via one well, produce fluids from the reservoir via the same well or one or more offset wells, and examine the produced fluid to determine if any of the injected oil is present therein. Instances in which control of an oil is inadvertently lost include theft and spillage of an oil.
Regardless of how control of a first oil is lost, it often occurs that one comes into control of a second oil, such as by producing an oil via a well penetrating a subterranean reservoir, or by locating a body of oil, which second oil is suspected of being or containing a portion of the first oil.
It is often difficult to compare a first oil and a second oil by chemical analysis. To facilitate such a comparison, it is known to add a tracer material to a fluid injected into a subterranean reservoir via a well and to examine a fluid subsequently produced from the reservoir via the same or a different well for the presence of the tracer material. Numerous materials have been suggested as tracer materials including radioactive materials, such as iodine.sup.131 and other chemical compounds not commonly present in reservoir fluids in significant concentrations and which are easily detected in small concentrations by conventional analytical techniques. In U.S. Pat. No. 4,141,692 to Keller there is described a composition of a liquid fuel, such as gasoline, containing certain types of chlorohydrocarbon or chlorocarbon tracers, which tracers can be detected by gas chromatography, using a pulsed electron capture detector. While known tracer materials have proven useful in many oil tracing methods, the need persists for a further improved method for tracing a first oil, particularly where the first oil is injected down a well, perhaps even out into the reservoir penetrated by the well, and a second oil is recovered via the same or another well in communication with the same reservoir and examined to see if the second oil is or contains a portion of the first oil.
Therefore, it is a principal object of this invention to provide a method for tracing an oil.
It is a further object to provide such a method wherein an oil-soluble tracer material is added to a first oil, control of the first oil is lost, and subsquently a second oil is located and analyzed for the presence of the tracer added to the first oil.
It is a still further object to provide such a method for evaluating the volume of reservoir oil produced from a well utilizing a hydraulic bottom hole piston pump actuated by a power fluid.
It is another object to provide such a method for investigating the dynamic conditions of fluid flow through a subterranean reservoir penetrated by one or more wells.
It is yet another object to provide such a method wherein the flow of an enhanced oil recovery fluid through the reservoir is monitored.
It is still another object to provide such a method wherein an oil or an oil base fluid containing a tracer material is injected into the reservoir via one well, reservoir fluids are produced via the same or a different well and the produced fluids are analyzed for the presence of the tracer material.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description and appended claims.